In a typical medical fluid therapy, a drug is administered into a blood vessel or the like of a patient via an infusion line from a container accommodating a drug, such as an infusion bag and an injector filled with a drug. In such a fluid therapy, there are cases in which the blood pressure of a patient is measured and monitored concurrently with drug administration as shown in FIG. 6. That is, a conventional infusion line consists of an injector 41 filled with a drug, a syringe pump 4 (a drug supplying part) for ejecting the drug from the injector 41, a tube member 7 for transporting the drug, and a puncture needle 9 provided at the end of the tube member and to be inserted into a blood vessel or the like of a patient for drug administration. Further, the infusion line is provided, at a midway point of the tube member 7, with a mixing/charging portion 8 which is adapted to enable blood sampling during treatment. The infusion line is also provided, in a line branched from a midway point of the tube member 7 and for supplying a drug solution to the patient's body, with a transducer 5 which is configured to convert the pressure in the infusion line into an electrical signal thereby providing an output to a pressure-value display means 6. Thus, a medical staff is allowed to constantly monitor the blood pressure of the patient by means of the pressure-value display means 6 while administering a drug. However, this type of blood pressure measuring systems had a drawback in that it was rather impossible, in practical use, to accurately monitor the pressure since the pressure in the tube member is affected by the pressure fluctuations of the syringe pump 4 upon administering a drug. This being the case, in order to overcome the drawback, there has been proposed an infusion line in which a flow control device is provided in midway of the line between the transducer 5 and the syringe pump 4. For example, in JP, A, 1-171527 or JP, A, 5-23308, there is proposed a flow control device having an entry path and an exit path, the entry path and the exit path being communicated through a communication path having a smaller cross section than those of the foregoing paths, characterized by being configured such that an elastic body is placed at the exit-path-side end portion of the communication path to close the exit-path-side end portion so that when the pressure of the fluid introduced from the entry path reaches a predetermined level, the elastic body is pressed to open the exit-path-side end portion and thus allowing the fluid to flow from the entry path to the exit path.
More particularly, the above described flow control device is comprised of: a first tubular member formed with the above described entry path thereinside and having a bulged portion at the tip end portion thereof; a second tubular member fitted to the first tubular member in such a way to surround the periphery of the bulged portion and defining the above described exit path in conjunction with the bulged portion; the above described communication path formed in the bulged portion; and a sealing member formed of an elastic material capped onto the bulged portion.
Further, as a flow control device, there is known a control device such as one used in the X line of the infusion line shown in FIG. 7. This flow control device used in the X line of FIG. 7 is configured to be integral with a transducer. The flow control device is provided with a path for flowing a fluid and a lever capable of changing the size of the path. This flow control device is to be used in such a way that the diameter of the path of the flow control device is significantly reduced for normal usage and the diameter of the path is increased upon a flushing operation thereby enlarging the path by controlling the lever.
Furthermore, in the above described infusion line, there is a case in which blood sampling for inspection is conducted from the mixing/charging portion 8 provided in the line during treatment. In such occasion, blood would remain in the tube member 7 between the patient and the mixing/charging portion 8 possibly leading to coagulation when left standing, and therefore it is necessary to return the blood to the patient side. This blood returning operation (generally called as a flushing operation) is performed by driving the syringe pump 4 to increase the flow rate of the drug thereby transporting the remaining blood to the patient. During this flushing operation, the pressure in the line is temporarily raised due to the actuation of the syringe pump 4 thus affecting pressure-value display means 6. Moreover, since the medical staff is supposed to be monitoring this pressure-value display means 6, the pressure-value needs to be reduced to a value accurately reflecting the patient's blood pressure soon after finishing the flushing operation. However, the flow control device described in each of the above mentioned patent publication had a problem in that it is difficult for a medical staff to accurately keep track of the blood pressure of a patient because it takes some time until a pressure rise in the line due to a flushing operation is eliminated. Moreover, the flow control devices disclosed in the above mentioned patent publications are configured such that a seal member having a tubular skirt is placed under a tension so as to come into intimate contact with the outer peripheral surface of the bulged portion, into which periphery the communication path opens, and this configuration makes it difficult to ensure a sufficient flow rate in a relatively low pressure range and to do so even at elevated pressures.
Further, the flow control device used in the X line of FIG. 7 is configured to change the diameter of the path through actuation of the lever, which significantly affects pressure readings of patient's blood pressure, thus raising concerns that there is too much burden on a patient such as infants, and besides it was difficult to obtain accurate pressure readings.